1. Field of the Disclosure
The present disclosure relates to a photoelectrochemical method for metal preservation, more specifically, it relates to a photoelectrochemical method for metal preservation by applying a coating containing nano-scaled titanium dioxide surface modified by nonionic surfactant on the metal surface.
2. Discussion of the Background Art
Great losses in all walks of life caused by metal corrosion account for about 3-4% of the national economic output. The modern anti-corrosion technology adopted may reduce the losses caused by corrosion by about 15%, which has considerable resource values and economic values.
Among those methods for controlling metal corrosion, the electrochemical cathodic protection and anodic protection are most effective ones. Typical examples of cathodic protection and anodic protection include, for example, cathodic protection of natural gas transmission pipelines, sacrificial anodic protection of transformer substation grounding network of a power system, gas phase cathodic protection of interior wall of storage tank, cathodic protection of bridge floor concrete, cathodic protection of petrochemical facilities, cathodic protection of shipping equipment, cathodic protection of long distance petroleum pipeline, and cathodic protection of crude petroleum storage tank, etc.
Materials used for grounding networks, for example, in the transformer substation grounding network of a power system, are mainly plain carbon steels in the form of flat steel or round steel. The grounding facilities, which have long been operated in a poor underground environment, suffer unavoidable chemical and electrochemical corrosions by soil, and stray current corrosion in stray current region of the earthing network. The corrosion of grounding network is generally shown in a local corrosion morphology. After the occurrence of corrosion, carbon steel materials of the grounding network are embrittled, exfoliated, loosened, or even fractured. With increased capacity of the electric power system and complexity of the network, as well as enhanced automation level, electric power accidents induced by the degraded performance of the grounding network gradually increase, and the damages and economic losses caused thereby also increase.
With growing concerns about anti-corrosion of the grounding network of the electric power system, anti-corrosion measures are widely taken at present in order to enhance or ensure the security level of the grounding network. Enlarged cross section of an grounding block and increased corrosion allowance can reduce negative impacts on the grounding effects exerted by corrosion, but cannot solve the problem radically, particularly in areas suffering severe corrosion, resulting in unnecessary consumption of large amounts of metal materials. Copper or other corrosion-resistant nonferrous metals may be used as grounding materials, whereas they are highly cost, difficult to construct, easy to cause galvanic corrosion, and further influencing safety of other steel structures. Composite materials such as galvanized steel, are usually employed as grounding materials, but the effect thereof won't be long lasting. The technique of cathodic protection has a favorable effect and a long protection period, and is convenient in construction. The method of sacrificial anodic electrochemical protection is suitable not only for newly-built grounding network protection, but also for reforming the old grounding network so as to prolong its life.
The method of sacrificial anodic protection or the method of applied power supply cathodic protection are effective in protecting the grounding network, however, aside from continuous consumption of sacrificial anodic metal blocks or electric energy, they further require instruments, apparatuses, conductors and the like for testing the protective current. Meanwhile, any failure of the monitoring devices such as a potentiostat in the protection system may lead to protection failure, and further result in serious corrosion of the grounding network.